Polymer/silica hybrid integration add-drop filter based on grating-assisted contradirectional coupler.

A polymer/silica hybrid integration add-drop filter based on a grating-assisted contradirectional coupler fabricated through simple and low-cost contact lithography is proposed. First, the structure pattern of the add-drop filter was formed in the lower silica cladding by contact lithography and inductively coupled plasma (ICP) etching. Then an SU-8 film was fabricated on top of it by a spin-coating method, and an inverted-rib waveguide structure was formed. Next, the slab layer of the inverted-rib waveguide was removed by ICP etching. We observe a rejection band with an extinction ratio of 13 dB and a 3 dB bandwidth of 0.6 nm at a wavelength of 1509.4 nm from the through port, and a passband with a side-mode suppression ratio of 12 dB and a 3 dB bandwidth of 0.5 nm at a wavelength of 1509.4 nm from the drop port. The shift of the passband with a temperature over the range of 25-55°C is approximately 4.8 nm. This temperature dependence exhibits an average slope of -0.16  nm/°C.